This invention relates to directional drilling, and in particular, though not exclusively, to such drilling in the oil and/or gas industries. The invention further relates to an improved downhole steerable motor assembly and related method.
In the drilling of deviated well bores in the oil and gas industry it is common practice to use downhole motors which incorporate a bend in the motor body to facilitate controlled deviation of the drilling assembly. Referring to FIG. 1 there is illustrated a prior art downhole motor, generally designated 5. As can be seen from FIG. 1, the motor 5 comprises a motor body comprising a bent housing 10, a motor power/drive section 15, and a thrust bearing package 20, the bent housing being fitted between the motor power/drive section 15 and the thrust bearing package 20. The bent housing motor 5 when used in conjunction with a suitable measurement and telemetry system allows a well bore to be deviated in a controlled manner using the so-called slide/rotate method. In the rotate mode a drill string (not shown) to which the bent housing 10 and motor section 15 are attached, is rotated during drilling and consequently the bend in the tool has no specific direction. The drilling process is effected by the motor 5 driving a drill bit (not shown), the direction of progress is nominally straight ahead although minor build or drop tendencies can be induced by appropriate selection of the sizes and placement of body stabilisers 25, 30. In the slide mode the motor body is not rotated, the bend in the body is aligned to face in a desired direction. Drilling is achieved using the motor 5 to drive the drill bit and the body is held in a nominal direction to cause the wellbore to deviate in a controlled manner.
Conventionally downhole motors are fitted with a thrust bearing package 20 to absorb hydraulic loading from the motor 5 and mechanical loads imposed during the drilling operation. Due to the limited diameter available in downhole equipment it is usually necessary to have a number of thrust stages to absorb these loads. Consequently, a finite axial length is required to house these thrust stages.
The most common type of motor used in the directional drilling industry is the Moineau type or a positive displacement motor (PDM) which has a universal coupling between the motor power section 15 and the thrust bearing package 20. This is necessary to allow the eccentric motion of a rotor to be converted into a co-axial rotation of a drill bit drive shaft. A universal joint is required to transmit power through the misalignment induced between the rotor and drill bit drive shaft, by the bend in the body. Therefore, it has become common practice to position the bend between the motor drive section 15 and the thrust bearing section 20.
The distance from the bent housing 10 bend axis to the face of the drill bit needs to be kept relatively short and this results in the length of bearing package and its thrust capacity (number of thrust stages) being restricted.
It is an object of the present invention to obviate or mitigate one or more of the aforementioned problems in the prior art.
According to a first aspect of the present invention there is provided a downhole motor assembly comprising a motor, at least one thrust bearing, and a bent portion, the assembly having a first end and a second end, the first end being closer to surface than the second end, in use, wherein the bent portion is closer to the second end than is the at least one thrust bearing.
The downhole motor assembly may also provide at least one further thrust bearing, wherein the at least one further thrust bearing is closer to the second end than is the bent portion.
In a preferred embodiment the at least one thrust bearing may be provided between the motor and the bent portion.
An at least one yet further thrust bearing may be provided, wherein the at least one further thrust bearing is closer to the first end than is the motor.
In an alternative embodiment the motor may be provided between the at least one thrust bearing and the bent portion.
In said alternative embodiment part of the motor may be provided closer to the second end than is the bent portion.
The motor may be provided within a motor drive section.
The at least one thrust bearing may be provided within a thrust bearing section.
The bent portion may comprise a bent housing.
Herein the term xe2x80x9cmotorxe2x80x9d is to be understood to mean at least one motor and may comprise a plurality of individual motors.
The motor may be of a hydraulic type.
The motor may be of a turbine type.
The motor may comprise a Moineau motor, PDM motor, or an electric motor.
The at least one thrust bearing may comprise at least one elastomer bearing.
The at least one thrust bearing may additionally or alternatively comprise at least one metal bearing.
A plurality of elastomer and/or metal bearings may be provided, the type and number being selected accorded to a required preselected thrust capacity.
The thrust bearing section may include a driveshaft.
The driveshaft may be flexible.
The driveshaft may thus be made from a resiliently flexible material. For example, the driveshaft may be made at least partially from titanium or copper beryllium steel.
Alternatively, the driveshaft may include one or more (and preferably at least two) swivel/universal joints.
The bent housing may include a driveshaft flexible coupling.
The second end may include an output shaft operably connected to the driveshaft.
The second end may further provide a bit connection means.
The motor assembly may provide at least one stabiliser on an outermost surface thereof.
The motor assembly may provide a first stabiliser at an end of the motor closer to the at least one thrust bearing than another end of the motor.
The motor assembly may provide a second stabiliser at or near the second end of the assembly.
The motor and the at least one thrust bearing may be coupled by a flexible coupling.
Where the motor comprises a plurality of individual motors one or more individual motors may be coupled one to the other by a further flexible coupling.
According to a second aspect of the present invention there is provided a method of directional drilling of a wellbore comprising:
providing a downhole motor assembly, the assembly comprising a motor, at least one thrust bearing and a bent portion, the assembly having a first end and a second end, the first end being closer to surface than the second end, in use, wherein the bent portion is closer to the second end than is the at least one thrust bearing;
directionally drilling the well bore by means of the assembly.